How Mast Cells Set Immune Defense on the Right Track

In the event of an infection, the immune system releases messenger substances. These molecules can either activate immune cells to defeat invading pathogens, or inhibit them to prevent an excessive immune reaction. For this, the immune system has to decide very quickly what mixture of activating and inhibiting messenger molecules leads to a successful defense.

Researchers from the Helmholtz-Centre for Infection Research in Braunschweig, Germany, have now been able to show that hitherto underrated immune cells, so-called mast cells, decide at a very early stage of an infection which way the defence has to go. They only produce the crucial messenger substance beta-interferon during a viral infection, not during a bacterial infection. The reason for this: While on the one hand the molecule always helps to defeat viruses, it hinders on the other hand important immune cells to kill bacteria -- and thus impairs the defence. The group's results have now been published in the Proceedings of the National Academy of Sciences.

Mast cells play a central role during allergic reactions, a function researchers have concentrated on until now. They reside directly under the skin and mucosae, and react immediately when an allergenic substance enters the body. As a result, reddened mucosae, swelling, runny eyes and a runny nose occur. However, mast cells also seem to have a crucial, but only superficially understood, function during pathogenic defence. "They wait precisesly at that position where pathogens enter the body," says Nelson O. Gekara, researcher in the group "Molecular Immunology" at the HZI, "and thus belong to the very first line of immune defence."